1. Field of the Invention
This invention relates generally to x-ray imaging systems with a C-arm which can be used for volume imaging. More specifically, this invention relates to scanning methods and algorithms used for volume reconstruction.
2. Background and Prior Art
Digital x-ray systems include C-arm volume imaging systems. These C-arm imaging systems have a source and detector that are 180 degrees opposite of each other at the ends of a C-arm. The C-arm itself is capable of being translated along the axis of the patient (the z-axis) (or the patient table can be translated) and capable of being rotated about that axis. The x-ray sources of these C-arm imaging systems can be modeled as projecting a cone of x-ray radiation through a volume of a patient to be detected by a detector having an area.
These C-arm imaging systems have been used to generate three dimensional reconstructions of volumes within patients. Such C-arm imaging systems usually rely on partial circle scans over an angular interval for 180 degrees plus the cone angle within a single plane. This angular interval typically ranges up to 200 degrees. Such a trajectory can exactly reproduce a disk with radius r inside the mid-plane define by the rotation of the line between the source and the detector center. However the volume outside the mid-plan only provides enough information for an approximate reconstruction.
In order to provide an exact reconstruction of an arbitrary volume within a patient, a complete source trajectory is required. A particular complete source trajectory can be seen in FIG. 1. as a “wobble.” Various other source trajectories have been combined to provide composites which are complete source trajectories and are well known in the art. Examples include a circle and line, two orthogonal circles, a circle and an arc, and a number of other trajectories which involve moving the source in a number of different dimensions. Once projections have been acquired over a complete source trajectory, an appropriate beam reconstruction algorithm can be used a known in the art.
However, the above complete source trajectories are impractical to achieve with the current C-arm imaging systems. Further it is preferable that the source move with a constant speed. This avoids significant complications in implementing the reconstruction algorithm. Accordingly, there remains a need in the art for a complete source trajectory which can be practically implemented in current C-arm x-ray imaging systems.